Stator construction for multi-stage axial-flow compressor



April 12, 1960 R. HART ET AL 2,932,442

STATOR CONSTRUCTION FOR MULTI-STAGEI AXIAL-FLOW COMPRESSOR Filed Nov. 14. 1955 2 Sheets-Sheet 1 R. HART ET AL Apr i! 12, 1960 STATOR CONSTRUCTION FOR MULTI-STAGEI AXIAL-FLOW COMPRESSOR Filed NOV. 14. 1955 2 Sheets-Sheet 2 United t tes Patent STATOR CONSTRUCTION FOR MULTI-STAGE AXIAL-FLOW COMPRESSOR Raymond Hart, Ockbroolr, and Derek Aubrey Roberts, Breadsall, England, assignors to Rolls-Royce Limited, Derby, England, a British company Application November 14, 1955', Seriai No. 546,696

Claims priority, application Great Britain November 22, 1954 9 Claims. (Cl. 230-122) This invention relates to multi-stage axial-flow com pressors, and is concerned primarily though not exclusively with axial-flow compressors used in gas-turbine en- :gines for aircraft propulsion.

vSuch compressors have. a stator casing which is of generally cylindrical form and which carries the rows of stator blades, and it has hitherto been the practice to construct the stator casings of the compressors of aircraft gas turbine engines of light alloy, eg of aluminium or magnesium alloy, for the. sake of strength, rigidity and lightness. However, owing to the high inlet temperatures and pressures experienced in high-speed aircraft, and owing to the development of compressors wherein high temperature and pressure rises occur, the use of light alloys at the compressor outlet is precluded due to the combined eifect of the relatively high temperature and pressure.

According to the present invention, therefore, a multistage axial-flow compressor has a stator casing comprising an upstream part in which the upstream rows of stator blades are mounted, a downstream inner part which forms a boundary of the working fluid passage and in which the downstream rows of stator blades are mounted, and a downstream outer part surrounding said downstream inner part to provide a space therebetween, said downstream outer part only being secured to adjacent structure by which the compressor is supported on its downstream side and said downstream outer part at least being formed from a high-strength material.

- In one preferred arrangement, the upstream part is constructed of a light alloy and both the downstream inner and outer parts are formed from a high-strength material. In a second preferred arrangement, the upstream part and the downstream inner part are made in one piece which is formed from a high-strength material, the downstream outer part being as stated formed from a high-strength material. Suitable high-strength materials include some ferrous alloys and titanium alloys.

According to a preferred construction of the invention said upstream part is made from a light alloy and separate from the downstream parts, and the upstream part is provided with a flange at its downstream end, and said downstream inner and outer parts are formed from high-strength material and are formed at their upstream ends with flanges or like bolt-receiving means, and the upstream part and the downstream inner and outer parts are secured directly together by bolts or the like with the flanges or the like in abutment.

According to another feature of the invention, said space between the downstream inner and outer parts is in communication with the working fluid passage at the delivery of the compressor, so as at least at the point of communication substantially to equalise the pressures on either side of the downstream inner part. Said space may form an annular manifold for tapping oif working fluid from the compressor; such tappedoff air may be used for a variety of purposes 'as is well-known, for examplefor anti-icing purposes, or for operating an air 2,932,442 Patented Apr. 12, 1960 surround a diffuser duct structure of the compressor, and.

the latter may comprise inner and outer annular walls of the working fluid passage interconnected by a plurality of radially-extending struts which extend outward beyond the walls to be secured to the outer part. In one arrangement according to this feature of the invention there may be provided means defining a manifold between the outer wall and the downstream outer part, said manifold being in communication with the interior of the struts to receive therefrom leakage air which has passed through a seal between the delivery end of the compressor rotor and adjacent stationary structure. The leakage air may be tapped off from the manifold for any suitable purpose.

Some constructions of multi-stage axial-flow compressor will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 is an axial section through part of the compressor,

Figure 2 is a section on the line 1I-II of Figure 1,

Figure 3 is a section on the line III-III of Figure 1,

Figure 4 is a section on the line IV-IV of Figure l, and

Figure 5 illustrates in axial section part of a second construction.

The compressor comprises a rotor 10 carrying at its periphery a number of rows of rotor blades 11. Rows of stator blades 12 alternate with the rows of rotor blades 11 and the stator blades 12 are carried by a stator casing which is formed in a number of parts 13, 15, 16.

The upstream part 13 of the casing, nearest the inlet of the compressor, is formed of light alloy e.g. aluminium alloy, and has grooves 14 machined in it, in which the stator blades 12 of the low-pressure stages are mounted. It will be appreciated that the part 13 has a considerable extent beyond that shown in the figure, for example there may be six further rows of blades 12 upstream of the row shown, each mounted in a similar groove 14.

The downstream inner part 15 is a fully-machined forged steel ring split into two parts on a diametral plane and is formed with a number of annular grooves 17 in which are mounted the rows of stator blades 12 of the high-pressure compressor stages, and the downstream outer part 16 is in the form of a cylindrical steel drum surrounding the blade-carrying part 15 in spaced relation thereto and extending away from the downstream end of the part 13 to axially beyond the downstream end of part 15.

The parts 13, 15, 16 of the stator casing are secured together in the following way. The parts 13, 15 are formed with outward, circumferentially-extending flanges 18, 19 respectively which have drilled holes therein, and the part 16 is formed with swellings 20 each of which is also formed with a drilled hole, in the base of which is a tapped hole of smaller diameter. Tubular locating dowels 21 extend through the drilled holes in the flanges 18, 19, into the larger-diameter portions of the holes in the swellings 2d, and bolts 22 extend through the dowels 21 and engage in the tapped holes in the swellings 20. The locating dowels 21 may be of oval form to allow for the relatively greater thermal expansion of the lightalioy part 13 of the stator casing than that of the steel parts 15, 16 as more fully described in United States of America Patent No. 2,764,266. The locating dowels 21 may be provided with beads each formed with a flat 23: to abut the casing to prevent their rotation in the drilled holes. As indicated in the drawing, when the parts are cold, there will be a clearance radially inward of the dowel 21 with respect to flange 18, and radially outwards of the dowel with respect to flange 19 and swelling 20, and the reversewill be thecase at the maximum temperature expected in operation.

The inner surfaces of the parts 13, and. of the platforms of the blades 12 carried thereby form the outer boundary of the working fluid passage of the compressor, and the surface of the rotor 16' forms the inner boundary of the passage in the vicinity of the blades 11, 12.

The compressor also comprises, as is usual, a diffuser duct structure, and in the latter the boundary of the working fluid passage is formed: by inner and outer annular sheet-metal walls 24, these walls diverge from one another in the direction of flow and, While slightly curved, may be considered as substantially frusto-conical, the smaller-diameter end of the outer wall 25 being its upstream end and the inner wall 24 having its smaller diameter at its downstream end.

The outer wall 25 has a ring 26 welded to its upstream end, which engages with the downstream end of the part 15 of the stator casing, and the inner wall 24 has welded to its upstream end a shroud ring 27 for the inner ends of the stator blades 12 of the last stage of the compressor.

The ring 26 is substantially of U-section, having a first annular flange 28 whichforms the boundary of the workingfluict passage and extends from the wall 25 towards, but stops short of, the part 15 to leave an annular gap therebetween, and having a longer outer annular flange 29 which slidingly engages over the downstream end of the part 15. The flange 29 is provided with circumferentially-spaced apertures 30.

Struts 31 extend radially outwards from the wall 24 through the wall 25 to the casing part 16 and the struts 31 are arranged to support the walls 24, 25 in position; there may be, for example, eight such struts. Each of the struts, which are of streamline section, has a main portion 32 which extends into a correspondingly-shaped aperture in the wall 24 and through a correspondinglyshaped aperture in the wall 25, the apertures having lips 34,. 35 respectively by which the walls 24, 25 are welded to the strut; each strut 31 also has a cap portion 36 which iswelded to and closes the outer end of the strut 31.

A pair of rings 37, 38 are welded to the inner surface of the inner wall 24 inthe planes of the front and rear ends respectively of the struts 31. The ring 37 has an inwardly-directed scalloped flange 39 (see Figure 2), and the ringr38is formed as the periphery of a frusto-conical diaphragm member The flange 39 has secured to it. a member 41 which has a frusto-conicalv diaphragm portion bolted at its inner periphery to the inner part of the member 40, and which also-has a stepped cylindrical. axially-downstream-extending portion which is bolted, at its end remote from flange 33, to the outer part of member 40. The members 41 41 support a bearing 42 for the compressor shaft 43, and also support suitable sealing members 44 which co-operate with the shaft. Also secured to flange 39 is the outer end of one arm of an annular V-section member 45, the other arm of which is secured to the inner end of a diaphragm 46, the outer end of which is secured to a flange extending inwardly from the shroud ring 27. At the junction of the member 45 and diaphragm 46 there is carried a sealing member 47 which co-operates with a labyrinth seal member 43 carried on the rotor 10. At the apex of the V-section member 45, which is inwardly directed, there is secured a further sealing member 49 which co-operates with the shaft 43.

Cooling air for the bearing 42 is supplied through the centre of shaft 43 and flows out through holes 50 in the shaft, and thence through holes 51 in the frusto-conical portion of the member 41- and holes 52 in the member 40, thus surrounding the bearing 42 to protect it against heating. 7 p

Leakage air from the high pressure end of the compressor which escapes past the labyrinth seal arrangement 47, 48 flows through holes 53 in the shorter arm of V-section member 45 and thence through apertures formed between the scalloped flange 39 and the member 41 secured to it, into the interior of the struts 31.

The outer wall 25 of the working fluid passage has a continuous circumferential baffle 54 secured on its outer side just upstream of the struts, and a series of partannular baffles 55 which extend between the struts 31 and are welded to their circumferentially-facing sides, at say one-third of the distance from the leading edge to the trailing edge of the struts. Each of the baffles 54, 55 is formed of an inner-sheet-metal piece flanged at its inner periphery and welded to the wall 25, and an outer machined. piece butt-welded or seam-welded to the sheetmetal piece. The baflles 54, 55 extend outwardly to the casing part 16, and define an annular manifold which is placed in communication with the interior of the struts 31 by means of. holes 56. In this manner the leakage air from the compressor is contained by the manifold, and a suitable outlet union (not shown) is provided, secured toa facing on the exterior of easing part 16, by which the leakage air istapped off to be" used for cooling the turbine or any other suitable purpose;

Forward of the balfle 54, there is a space between the stator casing parts 15, '16 which also forms an annular manifold and is in communication with the compressor outlet through the apertures 30. This manifold is particularly suitable for tapping off a relatively large quantity of air at a high pressure, such as is required for anti-icing purposes, or for operating an air turbine connected to drive auxiliaries associated with the" engine. A facing 66 is shown to which a suitable outlet union may be attached.

In assembly, the walls 24, 25, ring 27, struts 31 including their caps 36, rings 37, 38, with member 40 and baifles 54, 55 are welded together, and the member 41, member 45, diaphragm 46 and member 47 are then bolted to the assembly in that order.

The outer casing part 16 may now be slid over the assembly, and if desired the casing part 16 may have an interference fit with the baffles 54, 55 and caps 36. The struts 31 are located with respect to the outer casing part 16 by means of dowel pins 57 which extend through the part 16 and the cap portion 36 of the struts;'the head 55 of the dowel pin 57 is secured in position by one of the three setscrews 59 which secure each of the struts 31 to the part 16.

The outer air casing wall 60 of the combustion equipment is secured by setscrews 61 to a flange 62 on the downstream end of part 16, and the inwardly-directed flange of the air casing wall 60 is scalloped as's'een at 64 (Figures Q. and 3) to clear the setscrews 59 to permit withdrawal of the wall 60. Fuel injectors for the comv bustion equipment may be mounted on casing part 16.

It will be noted that the form of the casing part 16 is particularly well adapted to withstand the stresses ex perienced in operation, and also that the part 15' is only lightly stressed as it is subjected to substantially the same pressure on the outside as on the inside. In addition the bolting means by which the two halvesof ring 15 are secured together are only lightly loaded, permitting a con"- siderable saving of weight.

The part 13 may be formed of magnesium alloy instead of aluminum alloy, and the parts 15, 16 may be part 16, which as before will provide the sole means by which the compressor is supported from adjacent structure on its downstream side. In this case the upstream part 113 and the downstream inner part 115, which together support the stator blades 12, may be made of thin section from the inlet to the outlet of the compressor, as shown for the downstream part in Figure 1.

It will be seen that the invention provides a construction of stator casing for a multi-stage axial-flow compressor which is not only resistant to the high stresses involved at the elevated temperatures encountered in the present state of the art, and is exceptionally light and rigid, but which also provides manifolds for tapped-off air integrally within the engine structure.

We claim:

1. A multi-stage axial-flow compressor comprising a tubular stator blade-carrying structure having an inlet end and an outlet end; axially-spaced rows of stator blades supported by said tubular structure; circumferential flange means on the exterior of said tubular structure at a position intermediate the ends thereof; an outer cylindrical casing of high-strength material secured at one end to said flange means, extending downstream from said flange means and surrounding in radially spaced relation the portion of said tubular structure between said flange means and the outlet end, thereby to define an annular chamber externally of the tubular structure; a diffuser duct structure spaced radially inwards from and supported from said cylindrical outer casing at a position downstream of the outlet end of the blade-carrying structure, the outlet end of said blade-carrying structure being slidably supported by said diffuser duct structure.

2. A multi-stage axial-flow compressor according to claim '1, wherein the diffuser duct section has at its upstream end a pair of radially-spaced axially-extending circumferential flanges, of which the radially-outer flange is longer than the radially-inner flange, the radially inner flange extending towards the outlet end of the tubular blade-carrying structure but having its end axially spaced from the blade-carrying structure, and the radially outer flange encircling and being in sliding contact with the outlet end of the tubular blade-carrying structure to afford the sliding support thereof.

3. A multi-stage axial flow compressor as claimed in claim 1, wherein said blade-carrying structure comprises an upstream portion formed of light alloy material and a downstream portion of high-strength material, said circumferential flange means comprising a first flange on the downstream end of the upstream portion and a second flange on the upstream end of the downstream portion, said first and second flanges being secured together, and

wherein the outer cylindrical casing of high-strength material has its upstream end secured to said flanges.

4. A multi-stage axial-flow compressor as claimed in claim 1, wherein the tubular blade-carrying structure is made in one piece which is formed from a high-strength material and is of thin section.

5. A multi-stage axial-flow compressor as claimed in claim 1, wherein said annular chamber is in communication with the outlet end of the tubular blade-carrying structure substantially to equalize the pressures on either side of the blade-carrying structure adjacent the outlet end thereof.

6. A multi-stage axial-flow compressor as claimed in claim 5, comprising also means to with-draw working fluid from the compressor through said annular chamber.

7. A multi-stage axial-flow compressor as claimed in claim 1, wherein the outer cylindrical casing extends downstream to surround said diffuser duct structure, and the diffuser duct structure comprises inner and outer annlar walls of the working fluid passage interconnected by a plurality of radially-extending struts which extend radially outward beyond the annular walls to be secured to the outer casing.

8. A multi-stage axial-flow compressor as claimed in claim 7, comprising also a compressor rotor, a seal between the delivery end of the rotor and a space within the inner annular wall of the diffuser duct structure, means defining a manifold between the outer annular wall of the diffuser duct structure and the surrounding portion of the outer cylindrical casing, said manifold being in communication with the interior of the struts and the interior of the struts opening to said space within the inner annular wall, whereby leakage air which has passed through said seal into said space, flows through the struts into the manifold.

9. A multi-stage axial-flow compressor according to claim 8, wherein the means defining a manifold comprises a continuous circumferential baflie on the outer annular wall and extending outwards into contact with the outer cylindrical casing and a series of part-annular baflies extending circumferentially between the struts and radially from the outer annular wall to the outer cylindrical casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,698,287 Westgard Ian. 8, 1929 2,450,745 Baumann Oct. 5, 1948 2,488,783 Stalker Nov. 22, 1949 2,646,209 Galliot July 21, 1953 

